China is building airbases in the Spratly Islands of the South China Sea, dredging sand and dirt to create 2,000 acres of land where little more than rocky reefs existed before. Its biggest project is on Mischief Island, which sits less than 150 miles off the Philippines' Palawan Island but is 600 miles from China's own Hainan Island. Like virtually all the of the Spratlys, Mischief is claimed by more than one country. China says it owns them all. The United States objects.

China is ratcheting up the tension in the Spratlys. China's nationalist, Communist Party-controlled Global Times tabloid wrote this week that war between China and the United States would be "inevitable" if Washington continued to insist that Beijing stop its construction project. Yesterday China’s ambassador to Australia wrote an opinion piece for The West Australian newspaper that asserted China’s “indisputable sovereignty” over the islands.

All this over a bunch of islands? It sounds crazy. Why should we even care about the Spratly Islands?

The 35 islands and hundreds more reefs and guano-covered rocks are spread across an area the size of California but comprise less land area than San Francisco. The Chinese and Vietnamese think there might be great bonanzas of oil and gas there. The U.S. Energy Information Administration thinks the chance of that is roughly zero.

Indeed the Spratlys are not important for any oil and gas under them -- but rather because of the oil and gas (and everything else under the sun) that floats past them. More than half of world maritime trade passes through the South China Sea, with the world's busiest shipping lane passing right by the Spratlys. That includes billions of barrels of oil a year and hundreds of billions of cubic feet worth of liquefied natural gas. Control this flow and you control the energy security of Asia.

This week Beijing made the unprecedented admission that its construction project in the Spratly Islands is part of a military strategy that includes the extension of its naval strength beyond the mainland and into the open seas. China criticized the U.S. for “meddling” in the South China Sea and on Monday complained about a U.S. recon flight over the Spratlys.

A Pentagon spokesman defended U.S. movements there, reportedly saying: "All of our flights and all of our ship movements are through international airspace and international waters," said Col. Steve Warren. "This is part of our mission to defend freedom of navigation."

The animosity isn't new. Chinese vessels have harassed U.S. ships and aircraft in the region for years. In 2001 a Chinese fighter jet collided with a U.S. observation plane; the Chinese jet crashed and the American plane made an emergency landing on Hainan Island. China has had hundreds of more serious run ins with other countries that claim the Spratlys as their own, especially Vietnam. It was just a year ago when a Chinese deepwater drilling rig called the Haiyang Shiyou 981 began drilling in in another group of islands in the South China Sea called the Paracels, just 120 miles from the coast of Vietnam. In the ensuing naval standoff Chinese ships sank a Vietnamese trawler and anti-Chinese riots across Vietnam.

President Obama in April made it clear he intends to stand up for the little guys in the South China Sea. "Where we get concerned with China is where it is not necessarily abiding by international norms and rules and is using its sheer size and muscle to force countries into subordinate positions," he said at an event while traveling in Jamaica. "We think this can be solved diplomatically, but just because the Philippines or Vietnam are not as large as China doesn't mean that they can just be elbowed aside.”

It’s not obvious that the Spratlys should be under Chinese domain. They are more than 400 nautical miles from mainland China. Yet the strategic importance of this region to China cannot be understated. In the early 1990 Chinese Premier Deng Xiaoping proclaimed that in the South China Sea "sovereignty is ours, set aside disputes, pursue joint development."